1. Technical Field
The invention relates generally to body implantable leads for conducting electrical signals to and from tissue. More specifically, the invention relates to a lead fixation device made of an electrically conductive material that is selectively coated with an electrically insulating material to increase the impedance of the lead fixation device.
2. Background
Many implantable medical devices (“IMDs”) use body implantable leads (hereinafter “leads”) having one or more electrodes to deliver stimulation pulses to, or sense electrical impulses that are output from, tissue within a patient. An example IMD is a heart stimulation device, e.g., a pacemaker, a cardioverter, a defibrillator, or any other type of stimulating/sensing instruments, which uses one or more leads to deliver electrical stimulation pulses to a heart and to sense electrical impulses generated by the heart. Thus, the leads are used by the IMD to assist in the reversal, via defibrillation or cardioversion, of certain life threatening arrhythmias, or to stimulate, via pacing, the contraction of the heart.
During use, a microcontroller within the IMD interprets electrical signals that are sensed by the electrode(s). In response to the sensed electrical signals, the IMD's microcontroller can decide to pace or shock the heart via transmission of electrical energy from a power source, e.g., a battery, within the IMD through the lead and electrode(s), and into heart tissue. Thus, the lead functions as an electrical conduit through which electrical pulses can be delivered from the IMD to heart tissue and electrical signals that are sensed at the heart tissue can be delivered to the IMD.
Typically, a lead has a proximal end, which is configured to interface with the IMD, and a distal end, which includes the electrode(s) and is configured to contact tissue within the patient. During installation of the IMD and its associated lead(s), the distal end of each lead is inserted through the patient's venous system and into the patient's heart. After it is determined that the distal end of the lead is adjacent to a desired tissue location, a lead fixation device, e.g., a sharpened helix, located at the distal end is used to secure the distal end of the lead to the tissue. The lead fixation device can be made of a conductive material, and the lead fixation device can be electrically coupled to an electrode at the lead distal end. In these instances, the lead fixation device and/or the electrode can be used to emit and sense electrical signals.
When designing a lead electrode and/or lead fixation device that is to be implanted within a patient's body, one of the more important design requirements is that a high value of impedance exists at the interface between the tissue and the electrode and/or the lead fixation device. A high value of impedance at the interface is desirable because it decreases the amount of current necessary for stimulating the tissue, and consequently increases the life span of the IMD power source, e.g., battery, and therefore lengthens the over all life of the IMD.
It should therefore be appreciated that there is a need for a lead that includes a high-impedance lead fixation device that provides the lead with adequate mechanical stability, and does not excessively drain the IMD power, and thus, extends the life of the IMD. The present invention satisfies these needs.